Question

Two spheres, A & B, are made up of the same material. The radius of A is twice that of B, while the temperature of A is half that of B. What is their ratio of energy emitted per unit time (EA : EB)?

(a) 1

(b) 1/4

(c) 1/2

(d) 1/16

Answer 1

Correct choice is (b) 1/4

The best I can explain: Energy emitted per unit time is given by Ae.

e & σ will be the same for both.

 A = 4πr^2

 ∴ EA : EB= rA^2*TA ^2/rB^2*TB^4

= 4*1 / 1*16 = 1/4.